Processes and equipment for manufacturing surgical needles are well known in the art. Conventionally, wire on spools is straightened and cut into needle blanks. The needle blanks are then subjected to a series of conventional grinding, forming, shaping and drilling steps to form surgical needles having distal piercing points and proximal suture mounting ends. The distal ends of the needles may be either of the taper point type or the cutting edge type. The suture mounting end may have a formed channel or a drilled hole. The needles may be straight or curved. The piercing points may be sharp or blunt.
Conventional needle manufacturing equipment and processes are disclosed in European Patent Application Publication No. EP 650698 and U.S. Pat. No. 5,477,604 which are incorporated by reference.
It is typically required that conventional surgical needles have a smooth surface free from burrs, protrusions, machining marks, and other known surface irregularities. Such protrusions or surface irregularities may result from the needle manufacturing process. It can be appreciated by those skilled in the art that such protrusions or surface irregularities must be removed from a needle in order to have a needle with a smooth surface. It is believed that a smooth needle surface provides minimal tissue drag and decreased tissue trauma. In order to provide a needle free from protrusions and surface irregularities, it is known in the art to electropolish surgical needles. Electropolishing processes and an apparatus for electropolishing drilled surgical needles are disclosed in U.S. Pat. Nos. 3,707,452 and 3,701,725 which are incorporated by reference. A continuous electropolishing method is disclosed in U.S. Pat. No. 5,477,604.
In a conventional electropolishing process, a plurality of metal parts, e.g., surgical needles, is immersed in an aqueous bath containing an electrolyte such as acid and water, e.g., phosphoric acid and water. The bath typically is contained in a conventional, non-conductive vessel having a sufficient capacity to effectively contain the bath and metal parts. Two electrodes of opposite polarity are immersed in the bath and a current is conducted from the anodic electrode, through the metal parts and to cathodic electrode. The metal parts are typically in direct physical contact with the anodic electrode. The passage of current through the bath results in the removal of metal from the exterior surfaces of the metal parts, especially at sharp surfaces or irregular surfaces.
It is known in electrochemical processes that heating the electrochemical bath may facilitate the metal removal process. It is also typical to have some sort of mechanical agitation or circulation of the electropolishing bath. The pattern of metal removal in an electrochemical process is believed to be a function of several factors, including contact with the anode and/or other metal parts, orientation with respect to the cathode, and the configurations of the cathode. It is also believed that the activity of metal removal is affected by the specific gravity and "freshness" of the electropolishing bath.
Metal removal in an electropolishing process is believed to be caused by a known electrochemical reaction. Specifically, acid components, and some components of the metal have an affinity for each other. This is further enhanced by the current flow through the bath. As the metal is removed from the parts, a film is formed at the exterior surface of the parts. This film is believed to consist of a viscous liquid, which is saturated with the dissolution products of the metal, and a blanket of anodically discharged gas, typically oxygen. It is believed that this film does not perfectly conform to the exterior surfaces of part. Instead of following the micro-roughness, it tends to conform to the exterior macro-contour. Therefore the film is effectively thinner over small projections and thicker over depressions. Since there is correspondingly less resistance at the projections, more current is allowed to flow at those locations causing more intense localized polishing. This is believed to be one explanation of how surface roughness is smoothed during electrochemical polishing. It is also believed that temperature has an effect on the reaction rate, and, therefore, on the amount of metal removal. Typically, it is known to heat the electrolyte to some optimal temperature, for any particular electrolyte bath and surgical needle combination, for the desired metal removal rate.
Although the electropolishing processes of the prior art for surgical needles are adequate, there are certain disadvantages attendant with their use. Most conventional electropolishing processes are batch processes. In typical batch process, mechanical damage to the needles may result from the needles coming into contact with each other during handling and processing. Another disadvantage is that the metal removal rate is highly variable. For example, the suture mounting ends of the needle may experience excessive, detrimental metal removal. It is presently not possible to polish specific sections of a needle without polishing the entire needle. Another disadvantage is that the needles may experience different removal rates depending on their location within the bath with respect to the electrodes and with respect to the other needles. Yet another disadvantage is that metal removal rate may be affected in an adverse manner when needles contact each other in an electrochemical polishing bath.
There is continuing need in this art for improved electropolishing processes for surgical needles which would overcome these disadvantages.
Therefore, it is an object of the present invention to provide a novel continuous electropolishing process.
It is a further object of the present invention to provide an electropolishing process which allows the polishing of individual sections of a needle.
It is still another object of the present invention to provide an electropolishing process which provides reproducible, uniform metal removal.
Still yet another object of the present invention is to provide an electropolishing process which minimizes mechanical damage to surgical needles during processing.
Accordingly, a novel continuous process for electropolishing surgical needles is disclosed. In this process, surgical needles are mounted to a conductive carrier strip. The conductive carrier strip and needles are connected to an anodic electrode. The carrier strip moves the needles through an electropolishing bath contained in a vessel having a cathodic electrode therein so that at least a section of each needle is immersed and moved through the electropolishing bath. A current is passed between the anodic electrode, through the carrier and needles and to the cathodic electrode such that metal is removed from the exterior surfaces of the sections of the needles immersed in the bath. In particular, surface roughness is removed producing needles having smooth surfaces. The strip mounted polished needles are then moved out of the electropolishing bath.
Yet another aspect of the present invention is the above-described electropolishing process wherein the bath is caused to flow such that the direction of flow is 180 degrees opposite to the direction of movement of the carrier strip and needles for at least one half of the movement of the needles through the bath.
Still yet another aspect of the process of the present invention is the above-described electropolishing process wherein the bath is contained in a vessel having opposed end walls with an entrance opening in one end wall for the carrier strip and needles to enter the bath and an exit opening on the other end wall to allow the carrier strip and needles to exit the bath. The exit and entrance openings have bottoms and the level of the bath in the vessel is above the bottoms of the openings.
There are numerous advantages associated with the process of the present invention. First of all, it is now possible to electropolish surgical needles in an electropolishing process wherein the amount of metal removal on each needle is substantially constant for each needle processed through the bath. In addition, needles can be continuously electropolished without having individual needles contact each other since the needles are individually mounted to a carrier strip.
It is now possible using the process of the present invention to isolate the electropolishing to certain sections of the needles, thereby eliminating metal removal from sections in which it is not desired.
Other features and advantages of the invention will become more apparent from the following description and accompanying drawings.